Despite ample documentation of age-related changes in physiologic parameters, mechanisms governing the process of aging of the lungs have not been well studied. Among the identified age-associated changes is the modification of the extracellular matrix (remodeling). These changes result in alteration of the aged lungs response to injury and repair. As importantly, the number of senescent cells in the lungs increases with age. However, the mechanisms by which these cells provoke aging of the lungs are uncertain. All senescent cells are in growth arrest but continue to secrete large amounts of proteins that affect their microenvironment. Seemingly contradictory data indicate that, on the one hand, senescent fibroblasts are beneficial in wound healing but, on the other hand, limiting the number of senescent alveolar epithelial cells is beneficial in pulmonary fibrosis. Thus, there is a critical need to characterize the senescence profile of the various cells present in the lungs (mainly endothelial, epithelial, and fibroblast cells) to determine their relative contribution to he aging process. Despite the detection of senescent cells in aged lungs, their role in physiological remodeling associated with aging is unknown and their secretory phenotype remains undefined. Studying senescence in vivo has been technically challenging; however, we have recently obtained the p16-3MR transgenic system that empowers in vivo identification of p16ink4A+ cells (senescent cells) and their subsequent isolation by flow cytometry as well as their conditional deletion via the administration of gancyclovir. We propose to use this mouse model to more definitely define the role of senescent cells in lung aging; we will validate our data in nonhuman primate aging lungs, a translational model to human aging. We hypothesize that each senescent cell type (alveolar epithelial, endothelial and fibroblasts) has a characteristic secretory associated senescence profile to indicate their relative contribution to aging. Two specific aims are proposed to address this hypothesis: 1) To identify the senescence-associated secretory profile of each different senescent cell type (alveolar epithelial and endothelial cells and fibroblasts) to determine their contribution to lung tissue remodeling. Senescent and non-senescent cells will be isolated from non-lethally irradiated p16-3MR mouse lungs by flow cytometry and their transcriptional profiling will be determined. The expression of differentially expressed identified proteins will be validated in young and aged nonhuman primate lungs; and 2) To determine the contribution of senescent cells in the age-associated remodeling of the lungs. Using the p16-3MR transgenic mouse, we will determine whether the presence of senescent cells affects the remodeling process in the lungs by deleting p16ink4A+ cells after non-lethal dose irradiation. The data gathered with this project will characterize the secretory profile of various senescent cell types that have an important functional role in remodeling in the lungs but also in other organs such as the brain or the kidney (senescent endothelial cells and fibroblasts) and provide new information as to mechanism.